Cathode ray oscillograph



Dec. 14, 1937. l| p, KUEHNl '2,102,421

CATHODE RAY OSCILLOGRAPH Filed July l2, 1934 Fig. 3. Fig. Z.

Fig. 4,

Inventor: Hans E Kuehifxi,

Patented Dec. 14, 1937 UNITED STATES CATHODE BAY OSCILLOGRAPH Hans P.Kuehni, Schenectady, N. Y., assigner to General Electric Company, acorporation of New York Application July 12, 1934, semi No. 134,184

s Claims. (Cl. 25o-27.5)

My invention relates to cathode ray oscillographs and the like and itsobject is to provide a simple means for adjusting the position of thecathode ray beam of such apparatus without, however, interfering withits deflection in )esponse to the` phenomenon under investigation.

In a cathode ray oscillograph, a cathode ray or beam is thrown upon atracing surface, which may be an observing screen or photosensitive nlm,and is deected thereon by deflecting means such as for example voltagesimpressed upon deflecting plates which cause the ray to bend or deflectin response to the voltage variations. In this way, curves are obtainedwhich are representative of some phenomenon to which the deectingvoltages are responsive. Ordinarily, with no defiecting voltageimpressed upon the deflecting plates, the beam or ray strikes thetracing surface at its center, thus establishing a permanent zeroposition of the ray on such surface. Oftentimes, it is desirable tostart the tracing movement of the beam at some point other than thecenter of the surface in order to more fully utilize the tracing spaceavailable and it is the object of my invention to provide simple meanswhereby the initial or zero position of the beam may be adjusted in anydesired direction and at any desired distance from the center of thesurface without interfering with the subsequent measurement deflectionsof such beam.

In carrying my invention into effect, I employ a magnetic eld which isadjustable in its direction and strength for deflecting the cathode rayas desired before it strikes the tracing surface. This deection of theray is in addition to any deflection of the ray produced by the usualdeecting means and without interference therewith.

The features of my invention which are believed to be novel andpatentable will be pointed out in the claims appended hereto. For abetter understanding of my invention reference is made in the followingdescription to the accompanying drawing in which Fig. 1 illustrates theapplication of my invention to an ordinary cathode ray oscillographtube; and Figs. 2, 3, and 4 illustrate the nature of the magnetic fieldas adjusted for different results.

Referring now to Fig. 1, I have here illustrated a usual form of cathoderay tube without its circuit connections and with the addition of myinvention thereto. Ihe tube consists of a sealed glass envelope I0having in one end a. cathode and focusing means for emitting a cathoderay or beam represented at II. The cathode and focusing means, comonlycalled cathode ray gun, are not represented in detail but it will beunderstood that a suitable cathode ray gun is placed at the left centralend of the tube and cathode rays are shot toward the tracing surface I4.

The cathode ray beam passes down the length of the tube and is projectedupon a tracing surface I4 which is here represented as the end surfaceof the enlarged portion of the glass tube which surface is provided witha fluorescent screen to make the beam easily visible thereon.Ordinarily, the beam will strike the surface at its center I5. The tubeshown is provided with a pair of deflecting plates I6 for deflecting theray along a horizontal axis and a pair of deilecting plates I1 fordeflecting the ray along a vertical axis. 'I'hese plates are on oppositesides of the undeflected path of the ray on axes which are at rightangles to each other, and voltages responsive to the phenomenon to beinvestigated may be impressed upon these plates, causing the ray to bedeflected in a direction and by an amount which is proportional to thedirection and magnitude of the applied voltages in the two axes.Ordinarily, the plates IB are employed to sweep the ray across thehorizontal axis at a uniform rate while it is deflected in the verticalaxis by some voltage under investigation applied to plates I'I.

In order to utilize the tracing surface to the best advantage, it may bedesirable to start the tracing operation at point I8 instead of at pointI5. In this way, we may then apply a sweep voltage that would, actingalone, s'weep the ray across the horizontal or time axisA from I8 t0point'l9 while, at the same time, the ray may be deflected along avertical axis by applying alternating voltage across plates I'I,producing a resultant record such as is represented at 20 in Fig. 1without running oil the tracing surface or unduly crowding the completerecord on half of the available tracing surface.

In the example given, it is, therefore, desirable to shift the zeroposition of the cathode ray from point I5 to point I8 before startingthe tracing operation and this is accomplished by means of the presentinvention.

Substantially surrounding the tube III at a point between the two setsof deflecting plates I6 and I'I, I have provided a pair of C-shapedpermanent magnets 2I and 22. These permanent magnets may be made fromthin strips of cobalt steel bent into the shapes desired, having aninside curvature corresponding substantially to the curvature of theouter circular wall of the tube I0 at this point. They are positionedabout the cylindrical portion of the tube as segments of a band.

The two magnets have like poles facing each other at their ends whichare equally separated by a relatively small gap, such as is represented,

and these magnets are supported in this relation by a ring 23 made ofnon-magnetic material, such as brass, and provided with worm-gear teethin its outer surface. This worm gear meshes with a worm 23 which may berotated by the thumb piece 2l. The ring 23 and the two magnets 2| andy22 may thus be rotated as a unit about tube I0 as an axis. Since thepermanent magnets have like poles facing each other, they will produce aflux through the tube of the character represented by the arrows 29 inFig. 2, where the magnets are represented in outline by dotted lines.The relative dispositionl of the two magnets is such as to cause themagnetic eld crossing the tube to be of substantially uniform density,as represented by the arrows 29.

Now, as is known, a magnetic field will prduce a deflection of a cathoderay, the direction of deection being dependent upon the direction of thefield and the extent of the deection being proportional to the strengthof such field. Thus, in Fig. 2, the ray is deflected to the left fromthe center of the tracing screen to the point Il and Fig. 2 may beconsidered as the resulting action of the field upon the ray whenlooking at the large or viewing end of the tube and considering that theray is bent when it passes through the magnetic'eld opposite magnets 2|and 22 and diverges at an angle from the central axis of the tube atthis point to strike the tracing surface at point I0. The direction ofthe field and the resulting Adirection of bending of the cathode ray areadjusted as desired by rotating the axis of this eld by turning thethumb nut 24.

In Fig.- 3, the magnets have been rotated through an, angle of aboutforty-five degrees in a counter-clockwise direction as viewed from thelarge end of the tube and the ray is bent downward by a correspondingangle and strikes the tracing surface at point 30.

In Fig. 4, the field has been rotated by one hundred and eighty degreesfrom that represented in Fig. 2 and its direction reversed so as todeflect the ray to thevright to strike the tracing screen at point 3|.

' The amount of bending of the ray and the distance of the points Il,30, and 3| from the center of the tracing surface are dependent upon thestrength of the magnetic field through the tube and, to adjust thisstrength, I prefer to shunt more or less of the ux from the permanentmagnets by means o'f a soft iron shunting ring represented at ,25, alsosurrounding the tube i0, and adjustable lengthwise of the tube towardand away from the permanent magnet field assembly and in a planeparallel thereto by a rack 26 secured to the shunt and a plnion21 thatmay be rotated by the thumb piece 28. When the shunt ring 25 is movedclosely adjacent the field-producingmeans, itshunts substantially al1 ofthe flux thereof and, when moved away from the field-producing means,less and less of the eld is shunted and the eld strength through thetube increases. This shunting action is also represented in Figs. 2, 3,and 4 by the arrows between the shunt ring 25 and the permanent magnets2| and 22.

'Ihe shunt being symmetrical to the axis of the tube and also to theaxis of the field-producingl means, it practically does not disturb the.uniformity of the field through the tube for any given adjustment and,thus, I can produce a `uniform eld through the tube of any desirablestrength and of any desirable direction, and can, thus, place the zeroposition of the ray at any desired point on the tracing surface.

Fig. 3 represents an adjustment suitable for taking an oscillographrecord or observation arca-1.2i

where it is expected that the record will be produced mostly or entirelyabove the horizontal or zero-measurement axis. Here the ray is initiallyshifted to point 30'. A suitable sweep voltage applied to plates I6 willsweep the ray to the right so that the line 30-32 represents thehorizontal time axis and zero voltage across deflection plates I1, andthe curve 33 represents a record that may now be taken by applying avoltage of the character represented bythis curve across plates I1. Ifan attempt is made to take such a record with the apparatus adjusted forthe same sensitivity but without initially shifting the cathode ray fromthe center of the tracing screen, the upper and usually the mostimportant portion of the record would be lost. T'his illustrates anotherexample of the utility of the invention where the zero-measurement axisis adjusted parallel to itself to a lower position and the measurementaxis is shifted to the left to bring the record into a satisfactoryposition on the tracing surface.

In accordance with the provisions of the patent statutes I havedescribed the principle of operation of my invention together with theapparatus which I now consider to represent the best embodiment thereofbut I desire to have it understood that the apparatus shown is onlyillustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A cathode ray tube, a tracing surface therefor, means for projectinga cathode ray through said tube onto said surface, two sets of deflect-1ng means at different axial positions in said tube, one set fordeflecting the ray along one axis, and the other set for deilecting theray along a different axis, and means located external to the tube forproducing an adjustable but substantially uniform magnetic field throughsaid tube in any desired direction in a plane at right cathode raythrough the cylindrical .portion of said tube onto said surface, a pairof shaped permanent magnets positioned as segments of a circular bandclosely surrounding the cylindrical portion of said tube withtheir likepoles facing each other but spaced apart so as to produce asubstantially uniform unidirectional eld through said tube in a plane atright angles to its axis, and means for supporting said magnets in saidrelationship and rotating the same about the tube in said plane.

3. A cathode ray tube having a cylindrical portion, a. tracing surfacefor said tube, means for projecting a cathode ray through thecylindrical portion onto said surface, a pair of C-shaped permanentmagnets supported closely about the cylindrical portion of the tube assegments of a band with their like poles facing each other but equallyspaced apart at opposite ends to produce a substantially uniformmagnetic field through the tube in a plane at right angles to-its axis,and a ring of magnetic material surrounding said tube adjacent andparallel to the permanent magnet assembly and adjustable towards andaway therefrom to shunt a portion of the flux of said permanent magnetsto vary the field through the tube.

HANS P. KUEHNI.

